The environment of the present invention is that of articulated vehicles which consist of a load carrying trailer attached to a tractor by a device which is known as a fifth wheel coupling. The tractor comprises a chassis supported by two pairs of coaxial wheels, one pair of which is driven by a prime mover and the other pair being used for steering purposes. The tractor portion of the articulated vehicle is used as a mechanism to which a series of different trailers may be attached and transported. The trailers commonly constitute the prime storage space for products to be shipped or moved.
One of the common drawbacks in the articulated vehicle method of shipping involved the tendency of the trailer portion to "jackknife" during heavy deceleration or on slippery surfaces. This jackknifing occurs whenever the rear road wheels of the tractor portion are locked and skid in a direction transverse to the direction of travel thus causing the trailer portion to swing about the fifth wheel coupling which is used to connect the trailer to the tractor moving portion. Further, the jackknifing may cause the trailer to hit the side of the tractor thereby posing a serious threat to not only the tractor and trailer vehicle but any other traffic on the highway which may come into the path of the uncontrolled articulated vehicle.
The most common type of jackknifing occurs when there is either a difference in the coefficient of friction between the road and the tires of the trailer wheels as opposed to the tractor wheels when each is in a locked and skidding condition or when the front wheels of the tractor do not skid and a side force is applied to the skidding rear wheels of the tractor which causes an imbalance between the direction in which the tractor is proceeding and the trailer which is following it. This imbalance causes uncontrollable jackknifing.
Various proposals have been made for inhibiting or controlling the jackknifing action of articulated vehicle by a braking action between the tractor and trailer, and while some of these systems have been shown to be acceptable in use as discussed, for example, in the Hayes et al U.S. Pat. No. 3,874,699, they make no provision for controlled articulation after the brake has been applied. That is, the Hayes et al patent provides a brake disk which is secured to a turntable which is mounted on the tractor and which is used to prevent rotation of the turntable when the vehicle is being braked. While this tends to limit the jackknifing effect when the brake calipers are applied, it does not provide any flexibility when the brake is applied. This means that once the brake calipers are applied in order to prevent jackknifing, the tractor and trailer unit must proceed without any further articulation. Therefore, should the driver of the tractor have to negotiate a turn while the brake calipers on the fifth wheel where in operation the entire tractor and trailer unit must proceed in a straight line which if the load in the trailer is heavy enough will surely cause uncontrolled skidding.
Furthermore, the turntable of the Hayes patent adds an additional piece of equipment to be mounted on the tractor frame which, because of the increased thickness, makes it impractical for use with standard U.S. tractor and trailer combinations. In the event that the truck would be modified, the revision would involve a substantial expenditure on the tractor and trailer and as a consequence of that modification, the tractor could not be used with the standard trailers.
The improved anti-jackknifing device of the present invention provides not only a means of preventing jackknifing during braking operations, but also provides a flexibility which allows for controlled articulation between the trailer and the tractor while the disk brake is applied without affecting the ability of the tractor to be used with standard trailers.